This invention relates generally to a color printing machine, and more particularly concerns a printing machine in which a document is printed in at least two different colors wherein the colors are reproduced simultaneously on the document sheet.
Hereinbefore, multicolor copying was achieved by using a multicolor electrophotographic printing machine. In the process of electrophotographic printing, a photoconductive surface is charged to a substantially uniform potential. The photoconductive surface is image wise exposed to record an electrostatic latent image corresponding to the informational areas of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document. Thereafter, a developer mixture is transported into contact with the electrostatic latent image. Toner particles are attracted from the carrier granules of the developer mixture onto the latent image. The resultant toner powder image is then transferred from the photoconductive surface to a copy sheet and permanently affixed thereto. The foregoing generally describes a conventional black and white electrophotographic copying machine. With the advent of multicolor electrophotographic printing, the process was essentially repeated for three or four cycles. Thus, the charged photoconductive surface is exposed to filtered light image. The resultant electrostatic latent image is then developed with toner particles corresponding in color to the substractive primary of the filtered light image. For example, when a red filter is employed, the electrostatic latent image is developed with toner particles which are cyan in color. The cyan toner powder image is then transferred to the copy sheet. The foregoing process is repeated for a green filtered light image which is developed with magenta toner particles and a blue filtered light image which is developed with yellow toner particles. Each differently colored toner powdered image is sequentially transferred to the copy sheet in superimposed registration with the powder image previously transferred thereto. In this way, three toner powder images are transferred sequentially to the copy sheet. After the toner powder images have been transferred to the copy sheet, they are permanently fused thereto. Thus, color electrophotographic machines previously employed required three passes to produce a multicolor copy. This, of course, reduced the speed of the printing machine. A typical electrophotographic printing employing the foregoing process is manufactured by the Xerox Corporation under the model name 6500.
With the advent of ion projection devices, an electrostatic latent image can be deposed upon a charge receptor surface. The resultant charge pattern may then be developed in a conventional manner. A printing machine utilizing an ion projection system is a relatively simple device and less complex than those previously employed. Moreover, an ion projection apparatus may be employed in a multicolor electrophotographic printing machine. Various types of ion projection devices have been developed. These are described in U.S. Pat. No. 4,538,163, issued on Aug. 27, 1985 to Sheridon; U.S. Pat. No. 4,463,363, issued on July 31, 1984 to Gundlach et al; U.S. Pat. No. 4,409,604, issued on Oct. 11, 1983 to Fotland; U.S. Pat. No. 4,408,214, issued on Oct. 4, 1983 to Fotland et al; U.S. Pat. No. 4,365,549, issued on Dec. 28, 1982 to Fotland et al; U.S. Pat. No. 4,267,556, issued on May 12, 1981 to Fotland et al; U.S. Pat. No. 4,160,257, issued on July 30, 1979 to Carrish; and U.S. Pat. No. 4,155,093, issued on May 15, 1979 to Fotland et al. All of the foregoing patents describe various types of ion projection devices which may be employed in printing systems to produce a charge pattern on a charge receiving surface.
In the area of multicolor electrophotographic printing, it is highly desirable to simultaneously transfer all of the toner powder images to the copy sheet rather than having to do it sequentially. Various approaches have been devised to achieve the foregoing. The following disclosure appears to be relevant:
Xerox Disclosure Journal, Vol. 1, No. 7, July 1976, Page 29; Color Xerography With Intermediate Transfer, Author: J. R. Davidson.
Davidson describes a xerographic development apparatus wherein four different color toner powder images are developed on their respective photoconductive drums. Thereafter, each toner powder image is transferred to an intermediate web and subsequently transferred in superimposed registration with one another onto the copy sheet.